1 Answer
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What you describe is a standard server-client environment that is built in emacs. Just add into your emacs config this line:

(server-start)

This starts the emacs server when you first launch emacs. It works in both graphical emacs and within terminal.

Next you go to an other terminal window and launch emacsclient to connect to the server. If the first instance was graphical, use option -nw force opening inside the terminal. Now you have two views into same emacs instance and they naturally share buffers.